Comparative study of medicinal-plant-derived carbon nanoparticles: green synthesis, antioxidant behavior, and metal-ion sensing

This study presents a green nanotechnology approach for the eco-friendly, chemical-free synthesis of Carbon nanoparticles (CNPs) using five medicinal plants: Syzygium cumini, Holy Basil, Azadirachta indica, Psidium guajava, and Bergera koenigii, via a rapid microwave-assisted method. The resulting CNPs exhibit red fluorescence with strong absorption near 650 nm and quantum yields (up to 25.2%), making them attractive candidates for optical nanodevice applications. Detailed nanostructural and spectroscopic analyses confirmed quasi-spherical morphology (10–60 nm), amorphous carbon phases (XRD), and the presence of surface functional groups from bioactive plant metabolites (FTIR). These plant-derived nanomaterials exhibited strong antioxidant activity (DPPH and ABTS assays) and demonstrated excellent sensitivity and selectivity in fluorescence-based detection of toxic metal ions. Notably, P. guajava CNPs detected Ni²⁺ (LOD: 0.09 ppm), A. indica for Fe²⁺ (LOD: 0.11 ppm), Holy Basil for Fe²⁺ and Pb²⁺ (0.011 and 0.022 ppm), and S. cumini for Fe³⁺ (LOD: 0.012 ppm). Biocompatibility assessments revealed minimal cytotoxicity at low concentrations, with Holy Basil-derived CNPs being the most biocompatible. This work advances green nanotechnology by demonstrating a sustainable, multifunctional CNP platform with integrated optical, sensing, and biomedical capabilities highlighting its potential for environmental monitoring and bio-nanotechnology applications.